Method of making straw pulp for straw board



45 process.

60 presence of water and steam,

Patented July 28, 1931 PATENT OFFICE MAX ZIMMERMAN, OF LOGKPORT, NEWYORK METHOD OF MAKING- STRAW PULP FOR STRAW BOARD No Drawing.

-This invention relates, generally, to pulp and paper board making; andthe invention has reference, more particularly, to anovel method ofpreparing straw pulp for the manufacture of straw board, such as used inmaking corrugated paper board and for other uses.

Heretofore, it has been common practice to employ the lime process incooking straw to m be used in producing straw board. The straw boardproduced by the limeprocess is not en- I tirely satisfactory for manyuses owing to the relative softness of the fibres composing the same,and the consequent tendency of such board to disrupt or tear, whensubjected to forming operations, for example, when using straw board forforming corrugated sheets or boards. Soft fiber boards, produced by useof the lime process, while passing through present day high speedcorrugating machines are frequently disrupted or injured, resulting inan inferior and ofttimes useless product. Also, when using the limeprocess the knots of the straw are frequently either partially or whollyundigested so that it is,necessary to I remove these knots from the cookafter the same has been discharged from the rotary. To remove suchknots, the washing and beating processes, following the cooking of thestraw, are rendered more lengthy, difiicult and expensive, andfrequently more or less of the knots are not removed so that theysubsequently appear as blotches or spots in the finished paper product,thereby detracting from the appearance of the product and lowerlng itsvalue.

In my copending application, Ser. No.

442,463, filed April 7, 1930, I have disclosed a method whereby straw istreated with lime,

4o soda ash and sulphur in a rotary or other digester, to produce a pulphaving strong, tough fibres and adapted to e fabricated into a board offar greater strength and reliability than that produced by the old limeThe present invention discloses another novel method by means of whichstraw is treated with lime and salt cake with or without the addition ofa small quantity of soda ash in a rotary or other diglesterin the wereby pulp Application filed N ovember 10, 1930. Serial No. 494,697.

so produced has exceedingly strong fibres and which is especiallyadapted for manufacturing board to be used for corrugating purposes.

The principal object of the present invention is to provide 'a novelmethod of making straw pulp suitable for the manufacture of straw board,which method will cause the resulting board product to be composed ofhardened, tough and strong fibres, so that a straw board made by themethod possesses ample strength, elasticity and tenacity to enable thesame to be subject to normal operations, such as its passage throughhigh speed corrugating operations without disruption or other injury,the said board product being free from blotches or disfiguring marks.

Another object of the present invention lies in the provision of amethod for making straw pulp for the manufacture of straw board, whichmethod will materially increase the pulp yield over that of limeprocess, the said method serving to-thoroughly digest knots and otherhard fibre portions of the straw to Still another object of the presentinvention is to provide a method for making straw pulp suitable for themanufacture of straw board, which method consists in treating straw withchemicals in a rotary or other digester or container to' produce strawpulp which may be manufactured into straw board with but littlewashing,thereby reducing the washing period considerably and also reducin theloss of pulp 'and of chemicals, and re ucing the amount of slime andwaste products, whereby a reduction in the depreciation of cylinders andfelts is obtained resulting in a substantial "saving in cost.

Other objects of this invention, not at this time more particularlyenumerated, will be' whereupon the head of the rotary is closedapproximately 15,000 pounds.

and the rotary is then revolved for about a half hour, during whichperiod steam is admitted which acts to wilt or break down the strawsomewhat, thereby rendering the same more compact. The head of therotary is then opened and more straw is added, whereupon the head isagain closed and the charge again steamed or wilted as before. Thisoperation is repeated a number of times until the full amount of strawwhich the rotary is capable of taking has been added. When the rotaryhas been filled with its entire quota of straw, salt cake is introducedthereinto, whereupon the rotary head is again closed and the rotaryrevolved while the steam pressure therein is increased for the cookingoperation. The whole batch is cooked for about eight hours, more orless, whereupon the liquor is drained off, the charge is cooled, thehead removed and the charge dumped. The charge is then washed andproceeded with in the usual way to produce pulp suitable for makingpaper board.

Without restricting the invention to details, the following is given asan example of the method of the present invention. The rotary, digesteror other suitable container is charged with 400 pounds of dry straw,such as wheat, rye or oat straw. lVater is then added to the extent of2,000 gallons, whereupon 450 pounds of slaked lime is added. The rotaryhead is now closed and steam is admitted thereinto and the rotaryrevolved for about thirty minutes. The head of the rotary is then openedand about 2,000 additional pounds of straware added, whereupon therotary is again closed and the charged steamed down or wiltedflforanother thirty minutes while revolving the rotary. The rotary is thenopened and more straw'added, whereupon the charge is again steamed downwhile rotating the rotary. This cycle of operations is continued untilthe rotary has received its full quota or batch of straw, which in thepresant instance is Dry salt cake to the approximate amount of 450pounds is then introduced into the rotary.

The rotary is now closed and the batch is cooked for about eight hoursunder a steam pressure of from thirty to forty pounds per square inch,depending upon. the softness of the straw, the rotary being rotated allthe while. During the cooking process, the lime functions to loosen andseparate the incrust edmatters, such as starches, gums and silicatesfrom the cellulose of the straw, while the salt cake acts as a digestingagent to aid in loosening and separating the straw fibres and inbreaking down the knots of the strawinto fibres. The salt cake at thesame time acts to greatly toughen and harden the straw fibres and renderthem particularly valuable for use in making paper board for corrugatingpurposes, the said board being well capa ble of withstanding the desiredhigh speed forming operations, such e. g. as corrugating operations. Thelime and salt cake combine with the lignin and foreign matter of thestraw to form various soluble or semi-soluble compounds, the saidcompounds being ofa liquid nature and consequently easily washed fromthe straw fibres. Very little slime is produced by this process which isan advantage over the process of applicants copending application,wherein an appreciable quantity of slime is produced, necessitating morethorough washing. After cooking the batch, the liquid and steam areblown off, the rotary is opened and the stock dumped to be thereuponwashed, beaten and proceeded with in the usual way to produce strawboard.

When using, the pulp formed by the process of this invention, thewashing and heating steps are greatly simplified and shortened, becauseof the absence of slime in the pulp and also because of the absence ofknots or other undigested matter. Also, the absence of knots and suchforeign matter facilitates the formation of the paper web and greatlyreduces the depreciation of cylinders and felts. The paper so producedis of strong, even texture, of high quality and capable of being putthrough any type of high speed machine. No foul odors are present whenthe rotary is blown ofl.

Owing to the use of salt cake in the combination with the lime duringthe cooking process, the cellulose straw fibres are rendered more pure,are better separated and are far stronger and tougher than the fibresproduced by other methods. In some instances, a small amount of soda ashmay be usedtogether with the salt cake in the treatment of the straw,for example, when using the above proportions, 50 pounds of soda ashtogether with 400 pounds of salt cake may be used in lieu of 450 poundsof salt cake. However, the use of soda ash is not essential though thesame may be used to advantage when it is desired to produce a somewhatsofter fiber than that produced by the present process.

It is not intended to limit the invention to the relative proportions ofstraw, salt cake and lime mentioned, inasmuch as variations from theseproportions may be made, de-

pending upon the physical characteristics of the straw used. Also,additional quantities of lime and salt cake may be added during thecooking process in some instances.

and texture and is free of blotches or other disfiguring marks.

It is to be understood that the steps above recited are given for thepurpose of illustrating the invention and are not to be considered in alimiting sense. Modifications will occur to those skilled in the art,such for example, as the addition of an increased quantity of soda ash.It is intended to cover all such modifications that fall within thescope of the appended claims.

What is claimed is 1. A process of disintegrating' straw which consistsin first treating a minor quantity of straw with slaked lime and steamWhile agitating in a rotary, adding additional uantities of straw atintervals until a full atch is loaded into the rotary, and then addingsalt cake to the batch and then cooking the batch.

2. A process of disintegrating straw which consists in first treating aminor quantity of straw with slaked lime and steam while agitating in arotary, adding additional quantities of straw at intervals until a fullbatch is loaded into a rotary and then adding salt cake and a relativelysmall quantity of soda ash to the batch and then cooking the batch understeam pressure for about eight hours.

3. A cooking process for disintegrating straw, consisting in firstpartially disintegrating an initial quantity of straw b the applicationof slaked'lime and steam, a ding additional quantities of straw andsimilarly disintegrating the same until a total batch of straw isobtained, adding salt cake to this batch of straw, and then finallycooking the batch by the use of steam under pressure while agitating thebatch.

In testimony, that I claim the invention set forth above I have hereuntoset my hand this 20th day of October 1930.

MAX ZIMMERMAN.

